The invention relates to a method for operating a gas scrubber, in which a first feed gas is scrubbed in a first scrubbing installation and a second feed gas is scrubbed in a second scrubbing installation operated in parallel to the first, in each case with the same physically acting scrubbing medium, in order to dissolve sulfur components out of the feed gases containing hydrogen, carbon monoxide, carbon dioxide, and also carbonyl sulfide and/or hydrogen sulfide and to obtain desulfurized gas streams, wherein scrubbing medium streams loaded with sulfur components and co-absorbed carbon monoxide arise, and wherein the first feed gas, the carbon monoxide partial pressure of which is lower than that of the second, is scrubbed in the first scrubbing installation at a lower pressure than the second feed gas in the second scrubbing installation.
In addition, the invention relates to a device for carrying out the method according to the invention.
The wording that the two feed gases “are scrubbed with the same physically acting scrubbing medium” is not intended to state that the scrubbing media used must be chemically and physically identical. Rather, it means that the scrubbing media used consist of the same basic substance which, however, can be to a greater or lesser extent loaded with substances which have been separated off from a feed gas or both feed gases.
Methods and devices of the type in question are known, for example, from the patent applications DE19651282, DE102012016643 and DE102013001677, the contents of the disclosures of which are incorporated in their entirety by reference in the present description. They are used, for example, in order to produce crude hydrogen and a carbon dioxide-rich gas turbine fuel gas containing hydrogen and carbon monoxide from a synthesis gas. The synthesis gas for this purpose is separated into a first part and a second part, wherein the first part is converted by water gas shift before it is introduced into the first scrubbing installation in order to scrub out carbon dioxide and sulfur components, whereas the second part is fed without further treatment to the second scrubbing installation for separating off sulfur components. On account of the pressure drops occurring during the conversion, the first scrubbing installation is usually operated at a lower pressure than the second. In both scrubbing installations, in each case, a scrubbing medium stream loaded with sulfur components and carbon dioxide arises, whereas, at least in the first scrubbing installation, in addition, a scrubbing medium stream is generated which is only loaded with carbon dioxide. The loaded scrubbing medium streams are passed on to the regenerating part of the gas scrubber, where the dissolved substances are separated off in order to leave the gas scrubber in product or tailgas streams.
Although hydrogen and carbon monoxide have a significantly lower solubility coefficient than carbon dioxide and the sulfur components present in the synthesis gas with respect to the physically acting scrubbing medium used, which is preferably methanol, in the scrubbing of the synthesis gases, hydrogen and carbon monoxide are also unavoidably dissolved out of the scrubbing medium in small amounts. In order to prevent the yield of hydrogen and/or of carbon monoxide and hydrogen being reduced by this process termed co-absorption, and to avoid the co-absorbed substances passing into a product stream or tailgas stream via the regenerating part of the gas scrubber, according to the prior art, the scrubbing medium streams loaded in the scrubbing installations are cooled and, in a first regeneration step, in each case expanded into a separate expansion vessel to a pressure which is generally less than a third of the pressure at which the gas scrubbing is carried out. The co-absorbed substances are in this case substantially converted into the gas phase, whereas carbon dioxide and sulfur components remain dissolved in the scrubbing medium for the most part and are not separated off until subsequent regeneration steps. The completely regenerated scrubbing medium is recirculated to the two scrubbing installations and used again for synthesis gas scrubbing.
The gas phases from the expansion vessels which, in addition to hydrogen and carbon monoxide, also contain carbon dioxide and sulfur components are compressed and recirculated to the first synthesis gas upstream of the first scrubbing installation. In this manner, although a high product yield and also high purities of product streams and tailgas streams are achieved from the regenerating part of the gas scrubber, at the same time, the costs arising in particular for the compression required of the gas phases that are to be recirculated have a negative effect on the economic efficiency of the method.
The object of the present invention is therefore to specify a method and a device of the type in question that permit the disadvantages of the prior art to be overcome.